There is known a lubricating oil feeder of the sort disclosed in Japanese Patent Application (OPI) 146792/83. The following discussion of a known lubricating oil feeder, shown in modified form in FIG. 13, will be described using both the reference letters of FIG. 13 and the reference numbers of the Japanese Patent Application shown in parenthesis next to like parts. As shown in FIG. 13 hereof, the known lubricating oil feeder comprises an oil receiving unit a such as a bearing, air supply means b(2) connected to the oil receiving unit a through air supply pipes c, c'(3), and a bypass d(4) branching off from the air supply pipe c(3) and coupled to the air supply pipe c'(3) located nearby the oil receiving unit a(1). The bypass d(4) is equipped with an on-off valve e(5) intermittently turned on and off, an oil injection device h(7) having an oil supply source g, (6) and a mixing valve j(8). Such a lubricating oil feeder is designed to supply oil and air simultaneously to the oil receiving unit a(1) by controlling the operation of the on-off valve e(5) using a controller f(5a). In this manner, a small, fixed quantity of lubricating oil is intermittently discharged into the air supply pipe c'(3) and is carried to the oil receiving unit a(1) with the aid of an air flow. Reference character k(8a) denotes a check valve and characters m and n identify pressure gauges, not shown in the Japanese Patent Application.
A suitable quantity of non-misty lubricating oil is thus always continuously carried to the oil receiving unit a with the aid of the compressed air flow and, because the compressed air itself contributes to cooling the oil receiving unit a, the oil receiving unit a is kept in optimum rotational condition.
This conventional method of supplying lubricating oil makes it essential to ensure the presence of a supply of lubricating oil because the quantity of oil supplied at one time to the oil receiving unit a is extremely small. There actually have arisen cases, however, where the oil supply may become unsteady because of irregularities caused by a clogged nozzle at the tip of the air supply pipe c, valve trouble, or damage to the piping.
In order to guard against such irregularities, pressure gauges m, n are attached to the air supply pipe c and the bypass d, respectively, in locations nearby the air supply source b so that the irregularities may be detected by monitoring pointer movement. Nevertheless, there are still several problems. For example, whether or not the oil injection device h is effectively operating to cause a fixed quantity of lubricating oil to be discharged intermittently and regularly will not be detected in the location where the pressure gauge n is installed and correct data concerning the supply of lubricating oil to the oil receiving unit will also not be obtained. Also, lubricating oil is supplied to a plurality of units simultaneously and, for this reason, the air supply pipe c is equipped with branch pipes. Each branch pipe is provided with the bypass d having the oil injection device h attached thereto. The mixing valve j is arranged at the juncture of the bypass d and the air supply pipe c. In such a case, because the branch pipes are installed in parallel with each other, the pressure in the air supply pipe c will change only slightly if some problem occurs at one point in the air supply pipe c. The irregular oil supply to each oil receiving unit a is accordingly undetectable by monitoring pressure changes in the air supply pipe c through the pressure gauge m.